This application is based on and incorporates herein by reference Japanese Patent Application No. 2000-134938 filed on May 5, 2000 and Japanese Patent Application No. 2001-73578 filed on Mar. 15, 2001.
1. Field of the Invention
The present invention relates to a motor, and more particularly to a motor having a rotational sensor for measuring a rotational speed of a rotor thereof and also having a worm shaft that is connected to a rotatable shaft of the rotor through a coupling member, such as a clutch.
2. Description of Related Art
One type of motor for actuating a power window system, an electrically actuated sunroof system or the like includes a rotational sensor for measuring a rotational speed of a rotor of the motor. The rotational sensor includes a sensor magnet and a sensing element (Hall IC). The sensor magnet is secured around a rotatable shaft of the rotor in such a manner that the sensor magnet is accommodated in an unoccupied space within a motor case of the motor where an armature, a commutator, a bearing for rotatably supporting the rotatable shaft or the like is not located. The sensing element is secured to the motor case in such a manner that the sensing element faces the sensor magnet and outputs a pulse signal indicative of a rotational speed of the sensor magnet that rotates integrally with the rotor to an external control device.
In a case of the power window system, during upward movement of a vehicle window, if an obstruction (such as a human body) is clamped between, for example, the vehicle window and its window frame, a rotational speed of the rotor of the motor that drives the vehicle window changes. Based on the change in the rotational speed of the rotor, electric current supplied from the control device to the motor is stopped or reversed to stop or reverse the travel of the window.
The above-described type of motor further includes a speed reducing arrangement. The speed reducing arrangement includes a worm shaft coupled with the rotatable shaft and also has a worm wheel meshed with a worm of the worm shaft. Furthermore, this type of motor includes a coupling member, such as a clutch, that transmits rotation of the rotatable shaft to the worm shaft and prevents transmission of rotation of the worm shaft to the rotatable shaft.
In this motor, the motor case includes a generally cup-shaped yoke and a housing that is secured to an open end of the yoke. The yoke is made of a metal material and receives the rotatable shaft. The housing of the motor is made of a resin material and receives the worm shaft. The sensing element is preferably secured to a resin component that is arranged at a connection between the yoke and the housing for ease of installation. Thus, the sensor magnet that opposes the sensing element is accordingly placed at the connection between the yoke and the housing, i.e., at the connection (coupling member, such as the clutch) between the rotatable shaft and the worm shaft.
However, when the sensor magnet is secured around the rotatable shaft near the coupling member, such as the clutch, the rotatable shaft must have an extra length to accommodate the sensor magnet therearound. This causes an increase in the axial length of the motor, resulting in an increase in the size of the motor.
The present invention addresses the above disadvantages. Thus, it is an objective of the present invention to provide a motor that has a reduced size and includes a rotational sensor and a coupling member, such as a clutch, for coupling a rotatable shaft of a rotor with a worm shaft.
To achieve the objective of the present invention, there is provided a motor including a motor case, a rotatable shaft, a worm shaft, a coupling member and a rotational sensor. The rotatable shaft is rotatably supported by the motor case and is rotated upon actuation of the motor. The worm shaft is substantially coaxial with the rotatable shaft and is rotatably supported by the motor case. The coupling member includes a driving-side rotator and a driven-side rotator that is drivingly engageable with the driving-side rotator. The driving-side rotator is connected to the rotatable shaft to rotate integrally therewith. The driven-side rotator is connected to the worm shaft to rotate integrally therewith. The rotational sensor includes a sensor magnet and a sensing element. The sensor magnet rotates integrally with the rotatable shaft. The sensing element measures a rotational speed of the sensor magnet. The sensor magnet is secured to the driving-side rotator to rotate integrally therewith. The sensing element is secured to the motor case in such a manner that the sensing element opposes the sensor magnet.